This invention relates to methods and apparatus for measuring the concentration of specific ions in aqueous solutions, and more particularly to a membrane-containing sensor device for determining the concentration of dicyanoaurate anions in an electroless plating bath.
Ion-specific sensor devices for determining the concentration of various ionic species are known in the art. For example, Bychkov et al describes ion-selective electrodes for determining gold in cyanide solutions (Journal of Analytical Chemistry of the U.S.S.R., 31(a), (1976) pages 1543-1547). The membranes of Bychkov et al are liquid solutions of the ionic associate of tetraphenylarsonium and the dicyanoaurate ion (C.sub.6 H.sub.5).sub.4 As.sup.+ Au(CN).sup.-.sub.2 in various organic solvents. However, liquid membranes have several disadvantages. For example, they often take the form of very complicated structures which have to be constantly replenished with fluids, thereby making them impractical for many large-scale industrial applications.
Solid membranes based on poly(vinyl chloride) (PVC) have been prepared for use in the past as ion selective membranes. However, these types of membranes are plasticized and lack the ruggedness and durability required for many long-term, large-scale industrial plating processes.
A different type of solid ion-specific membrane is described in U.S. Pat. No. 3,743,588, issued July 3, 1973 to Brown et al. The membrane of Brown et al is used for biomedical applications and include a hydrophobic elastomeric polymer and a hydrogen ion-carrier which is an uncoupler known to uncouple oxidative phosphorylation in mitochondria and chloroplasts. Similarly, U.S. Pat. No. 3,767,553, issued Oct. 23, 1973 to Brown et al, discloses a potassium ion-specific membrane comprising a mixture of a hydrophobic elastomeric polymer and a potassium ion-specific carrier. However, the prior art fails to describe or contemplate the use of such solid membranes to determine the concentration of dicyanoaurate anions (hereinafter also referred to as Au(CN).sup.-.sub.2 anions) in gold-containing solutions.
It is therefore an object of this invention to provide an improved membrane for determining the concentration of dicyanoaurate anions in a solution.
An additional object of the present invention is to provide an ion-selective membrane which is not substantially affected by electrical interference.
Yet another object of the present invention is to provide a durable, practical electrolytic device for determining the concentration of dicyanoaurate anions in an electroless gold plating bath.
It is still another object of this invention to provide an improved method for determining the concentration of dicyanoaurate anions in a gold plating bath.
These and other objects of the invention, together with the features and advantages thereof, will become apparent from the following description of the invention.